在開發客戶端與服務端的應用當中,數據交換介面通常都是通過XML格式來進行數據交換的.近年來,隨著AJAX技術的興起,JSON作為一種輕量級的數據交換格式,以其易於閱讀和編寫的優點,也越來越多的被使用到各個項目中.在OPhone SDK中,也提供了JSON的類庫方便對JSON格式的數據進行處理.本文將快速講解 JSON 格式,並通過代碼示例演示如何分別在客戶端和伺服器端進行 JSON 格式數據的處理.
什麼是JSON
JSON(JavaScript Object Notation)是一種輕量級的數據交換格式,易於閱讀和編寫,同時也易於機器解析和生成,非常適合於伺服器與客戶端的交互.JSON採用與編程語言無關的文本格式,但是也使用了類C語言的習慣,這些特性使JSON成為理想的數據交換格式.
和 XML 一樣,JSON 也是基於純文本的數據格式.由於 JSON 天生是為 JavaScript 準備的,因此,JSON 的數據格式非常簡單,您可以用 JSON 傳輸一個簡單的 String,Number,Boolean,也可以傳輸一個數組,或者一個複雜的 Object 對象.
String,Number 和 Boolean 用 JSON 表示非常簡單.例如,用 JSON 表示一個簡單的字元串 「 abc 」,其格式為:"abc".
除了字元 ",,/ 和一些控制符(b,f,n,r,t)需要編碼外,其他 Unicode 字元可以直接輸出.下圖是一個 String 的完整表示結構:
圖1.String的完整表示結構
一個 Number 可以根據整型或浮點數表示如下:
圖2.Number 的表示結構
這與絕大多數編程語言的表示方法一致,例如:
12345(整數)
-3.9e10(浮點數)
Boolean 類型表示為 true 或 false .此外,JavaScript 中的 null 被表示為 null,注意,true、false 和 null 都沒有雙引號,否則將被視為一個 String .
JSON 還可以表示一個數組對象,使用 [] 包含所有元素,每個元素用逗號分隔,元素可以是任意的 Value,例如,以下數組包含了一個 String,Number,Boolean 和一個 null:
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["abc",12345,false,null]
["abc",12345,false,null]
Object 對象在 JSON 中是用 {} 包含一系列無序的 Key-Value 鍵值對錶示的,實際上此處的 Object 相當於 Java 中的 Map<String, Object>,而不是 Java 的 Class .注意 Key 只能用 String 表示.例如,一個 Address 對象包含如下 Key-Value:
city:Beijing
street:Chaoyang Road
postcode:100025(整數)
用JSON 表示如下:
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{"city":"Beijing","street":" Chaoyang Road ","postcode":100025}
{"city":"Beijing","street":" Chaoyang Road ","postcode":100025}
其中 Value 也可以是另一個 Object 或者數組,因此,複雜的 Object 可以嵌套表示,例如,一個 Person 對象包含 name 和 address 對象,可以表示如下:
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{"name":"Michael","address":
{"city":"Beijing","street":" Chaoyang Road ","postcode":100025}
}
{"name":"Michael","address": {"city":"Beijing","street":" Chaoyang Road ","postcode":100025} }
一個實際例子
接下來,我會通過一個例子來詳細說明OPhone客戶端程序如何訪問服務端的介面程序讀取用戶列表數據,並在模擬器上顯示用戶列表數據.
1、服務端介面程序
,我們創建一個名為User的JavaBean作為用戶對象類,用來保存演示數據.
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public class User {
private int id;
s=keyword>private String name;
private String email;
private String gender;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
}
public class User { private int id; private String name; private String email; private String gender; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } }
接下來,我們創建一個名為JSONDemoServlet的Servlet類來作為服務端的介面程序.在這個程序里,定義了一個List對象用來保存用戶列表.
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private List<User> list;
private List<User> list;
客戶端程序訪問伺服器端介面時,介面通過prepareData方法為用戶列表初始化數據,添加用戶數據到List對象中.
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private void prepareData(){
list = new ArrayList<User>();
&nbs p;
User bean1 = new User();
bean1.setId(1001);
bean1.setName("Tony");
bean1.setEmail("tony@toeach.net");
bean1.setGender("male");
list.add(bean1);
……
}
private void prepareData(){ list = new ArrayList<User>(); User bean1 = new User(); bean1.setId(1001); bean1.setName("Tony"); bean1.setEmail("tony@toeach.net"); bean1.setGender("male"); list.add(bean1); …… }
接著遍歷用戶列表,把列表中的每個Java用戶對象轉換為JSONObject對象,再加入到JSONArray中去.
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JSONArray array = new JSONArray();
for(User bean:list){
//單個用戶JSON對象
JSONObject obj = new JSONObject();
try{
obj.put("id", bean.getId());
obj.put("name", bean.getName());
obj.put("email", bean.getEmail());
obj.put("gender", bean.getGender());
} catch (Exception e) {}
array.put(obj);
}
JSONArray array = new JSONArray(); for(User bean:list){ //單個用戶JSON對象 JSONObject obj = new JSONObject(); try{ obj.put("id", bean.getId()); obj.put("name", bean.getName()); obj.put("email", bean.getEmail()); obj.put("gender", bean.getGender()); } catch (Exception e) {} array.put(obj); }
,通過 Servlet輸出 JSON 時,需要設置正確的 MIME 類型和字元編碼.假定伺服器使用 UTF-8 編碼,則可以使用以下代碼輸出編碼后的 JSON 文本:
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response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
out.write(array.toString());
out.flush();
out.close();
JSONDemoServlet.java的完整代碼如下:
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.json.JSONArray;
import org.json.JSONObject;
public class JSONDemoServlet extends HttpServlet{
private static final long serialVersionUID = -7368225680407826408L;
private List<User> list;
/**
* 處理post方式提交的數據
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
doGet(request,response);
}
/**
* 出來get方式提交的數據
*/
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
//準備用戶數據
prepareData();
//JSON數組
JSONArray array = new JSONArray();
for(User bean:list){
//單個用戶JSON對象
JSONObject obj = new N> JSONObject();
try{
obj.put("id", bean.getId());
obj.put("name", bean.getName());
obj.put("email", bean.getEmail());
obj.put("gender", bean.getGender());
} catch (Exception e) {}
array.put(obj);
}
//輸出
out.write(array.toString());
out.flush();
out.close();
}
private void prepareData(){
list = new ArrayList<User>();
User bean1 = new User();
bean1.setId(1001);
bean1.setName("Tony");
bean1.setEmail("tony@toeach.net");
bean1.setGender("male");
list.add(bean1);
User bean2 = new User();
bean2.setId(1002);
bean2.setName("Jack");
bean2.setEmail("jack@hotmail.com");
bean2.setGender("male");
list.add(bean2);
User bean3 = new User();
bean3.setId(1003);
bean3.setName("Marry");
bean3.setEmail("marry@163.com");
bean3.setGender("female");
list.add(bean3);
User bean4 = new User();
bean4.setId(1004);
bean4.setName("Linda");
bean4.setEmail("linda@21cn.com");
bean4.setGender("female");
list.add(bean4);
}
}
response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
out.write(array.toString());
out.flush(); out.close();
JSONDemoServlet.java的完整代碼如下:
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.json.JSONArray;
import org.json.JSONObject;
public class JSONDemoServlet extends HttpServlet{
private static final long serialVersionUID = -7368225680407826408L;
private List<User> list; /** * 處理post方式提交的數據 */
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request,response);
} /** * 出來get方式提交的數據 */
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
//準備用戶數據
prepareData();
//JSON數組
JSONArray array = new JSONArray();
for(User bean:list){ /
/單個用戶JSON對象
JSONObject obj = new JSONObject();
try{ obj.put("id", bean.getId());
obj.put("name", bean.getName());
obj.put("email", bean.getEmail());
obj.put("gender", bean.getGender());
}
catch (Exception e) {}
array.put(obj);
}
//輸出
out.write(array.toString());
out.flush(); out.close(); }
private void prepareData(){
list = new ArrayList<User>();
User bean1 = new User();
bean1.setId(1001);
bean1.setName("Tony");
bean1.setEmail("tony@toeach.net");
bean1.setGender("male");
list.add(bean1);
User bean2 = new User();
bean2.setId(1002);
bean2.setName("Jack");
bean2.setEmail("jack@hotmail.com");
bean2.setGender("male");
list.add(bean2);
User bean3 = new User();
bean3.setId(1003);
bean3.setName("Marry");
bean3.setEmail("marry@163.com");
bean3.setGender("female");
list.add(bean3);
User bean4 = new User();
bean4.setId(1004);
bean4.setName("Linda");
bean4.setEmail("linda@21cn.com");
bean4.setGender("female");
list.add(bean4);
}
}
把該Servlet部署到Tomcat下,在瀏覽器輸入介面地址http://localhost:8080/article/JSONDemoServlet,輸出結果如下:
[{"id":1001,"email":"tony@toeach.net","name":"Tony","gender":"male"},{"id":1002,"email":"jack@hotmail.com","name":"Jack","gender":"male"},{"id":1003,"email":"marry@163.com","name":"Marry","gender":"female"},{"id":1004,"email":"linda@21cn.com","name":"Linda","gender":"female"}]
2、手機客戶端程序
準備好服務端的介面后,接下來就是準備寫客戶端的程序了.打開Eclipse新建一個OPhone項目.我們創建一個名為MainActivity的Activity類,如下圖所示:
要訪問外部網路,要在AndroidManifest.xml文件里增加一行安全許可:
<uses-permission android:name="android.permission.INTERNET"/>
這樣我們的應用程序就可以訪問網路了.
接著修改布局文件reslayoutmain.xml,增加一個TextView對象,用來顯示解析后的用戶數據.
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<?xml version="1.0" encoding=N>"utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView android:id="@ id/textView"
android:layout_width="fill_parent"
android:layout_height="fill_parent"/>
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <TextView android:id="@ id/textView" android:layout_width="fill_parent" android:layout_height="fill_parent"/> </LinearLayout>
OPhone SDK提供了Apache的HttpClient類處理網路訪問,相信很多讀者朋友都在其他項目當中用到過HttpClient.我寫了一個方法,獲取某一網址的網頁內容,代碼如下:
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/**
* 獲取網址內容
* @param url
* @return
* @throws Exception
*/
private String getContent(String url) throws Exception{
StringBuilder sb = new StringBuilder();
HttpClient client = new DefaultHttpClient();
HttpParams httpParams = client.getParams();
//設置網路超時參數
HttpConnectionParams.setConnectionTimeout(httpParams, 3000);
HttpConnectionParams.setSoTimeout(httpParams, 5000);
HttpResponse response = client.execute(new HttpGet(url));
HttpEntity entity = response.getEntity();
if (entity != null) {
BufferedReader reader = new BufferedReader(new InputStreamReader(entity.getContent(), "UTF-8"), 8192);
String line = null;
while ((line = reader.readLine())!= null){
sb.append(line "n");
}
reader.close();
}
return sb.toString();
}
/** * 獲取網址內容 * @param url * @return * @throws Exception */ private String getContent(String url) throws Exception{ StringBuilder sb = new StringBuilder(); HttpClient client = new DefaultHttpClient(); HttpParams httpParams = client.getParams(); //設置網路超時參數 HttpConnectionParams.setConnectionTimeout(httpParams, 3000); HttpConnectionParams.setSoTimeout(httpParams, 5000); HttpResponse response = client.execute(new HttpGet(url)); HttpEntity entity = response.getEntity(); if (entity != null) { BufferedReader reader = new BufferedReader(new InputStreamReader(entity.getContent(), "UTF-8"), 8192); String line = null; while ((line = reader.readLine())!= null){ sb.append(line "n"); } reader.close(); } return sb.toString(); }
修改MainActivity.java,在onCreate方法里增加解析服務端介面內容的代碼,如下所示:
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@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
try{
StringBuffer sb = new StringBuffer();
//在測試過程中,經常是用本機做測試伺服器,訪問本機的IP地址要設置為10.0.2.2
String url = "http://10.0.2.2:8080/article/JSONDemoServlet";
String body = getContent(url);
JSONArray array = new JSONArray(body);
for(int i=0; i<array.length(); i ){
JSONObject obj = array.getJSONObject(i);
sb.append("id:").append(obj.getInt("id")).append("t");
sb.append("name:").append(obj.getString("name")).append("rn");
sb.append("gender:").append(obj.getString("gender")).append("t");
sb.append("email:").append(obj.getString("email")).append("rn");
sb.append("----------------------rn");
}
TextView textView = (TextView)findViewById(R.id.textView);
textView.setText(sb.toString());
}catch(Exception e){}
}
@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); try{ StringBuffer sb = new StringBuffer(); //在測試過程中,經常是用本機做測試伺服器,訪問本機的IP地址要設置為10.0.2.2 String url = "http://10.0.2.2:8080/article/JSONDemoServlet"; String body = getContent(url); JSONArray array = new JSONArray(body); for(int i=0; i<array.length(); i ){ JSONObject obj = array.getJSONObject(i); sb.append("id:").append(obj.getInt("id")).append("t"); sb.append("name:").append(obj.getString("name")).append("rn"); sb.append("gender:").append(obj.getString("gender")).append("t"); sb.append("email:").append(obj.getString("email")).append("rn"); sb.append("----------------------rn"); } TextView textView = (TextView)findViewById(R.id.textView); textView.setText(sb.toString()); }catch(Exception e){} }
總結
本文簡單介紹了JSON的相關知識,以及在OPhone平台中如何通過JSON來和服務端的應用進行數據交換.
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